Shift control system for selecting between two shift patterns based on torque converter judders in an automatic transmission

Abstract

A shift control system controls an automatic transmission of a vehicle wherein half-lock-up control for a lock-up clutch is executed when the running state of the vehicle is in a predetermined operative range. The shift control system includes a half-lock-up control inhibiting unit for inhibiting the half- Lock-up control from being executed when the running state of the vehicle is held in a specific operative state even though the running state of the vehicle is in the predetermined range, a determining unit for determining whether or not the half-Lock-up control is inhibited by the half- lock-up control inhibiting means, and a controlling unit for controlling the automatic transmission such that a low speed stage at which the half-lock-up control is easily executed is positively utilized when it is determined that the half-lock-up control is not inhibited by the determining unit, and moreover, controlling shift change of the automatic transmission such that a high speed stage having a gear ratio lower than that at the lower speed stage is positively utilized when it is determined that the half-lock-up control is inhibited by the determining unit.

What is claimed is: 
     
       1. A shift control system for an automatic transmission of a vehicle, the transmission including a lock-up clutch, comprising: means for storing at least two different shift patterns for shifting the transmission as a function of vehicle conditions including vehicle speed, one of the patterns setting a higher speed stage having a lower gear ratio for the transmission and another of the patterns setting a lower speed stage having a higher gear ratio for the transmission;   means for selecting a first of said shift patterns;   means for determining whether a half lock-up control of the lock-up clutch is to be inhibited; and   means for selecting a second shift pattern from amongst said shift patterns as a shift pattern for controlling the transmission as a function of an output of said determining means, such that only said one of said shift patterns is selected when the half lock-up control is inhibited, wherein said determining means include detecting means for detecting judder of the lock-up clutch.   
     
     
       2. The shift control system according to claim 1 wherein the determining means includes a means for selecting the shift pattern setting a higher speed stage having a lower gear ratio when the half lock-up control is inhibited. 
     
     
       3. A shift control method for an automatic transmission of a vehicle, the transmission including a lock-up clutch, comprising the steps of: storing at least two different shift patterns for shifting the transmission as a function of vehicle conditions including vehicle speed, one of the patterns setting a higher speed stage having a lower gear ratio for the transmission and another of the patterns setting a lower speed stage having a higher gear ratio for the transmission;   selecting a first of said shift patterns;   determining whether a half lock-up control of the lock-up clutch is to be inhibited; and   selecting a second of said shift patterns as a shift pattern for controlling the transmission as a function of an output of said determining means, such that only said one of said shift patterns is selected when the half lock-up control is inhibited, wherein said determining step comprises a step of detecting judder of the lock-up clutch.